The subject matter disclosed herein generally relates to digital radio receivers and in particular to bit timing recovery methods and systems for such receivers.
In digital communication systems, transmission signals are produced by the modulation of a carrier signal with digital data to be transmitted. The digital data is commonly transmitted in packets wherein each packet includes a number of data bits. After the transmitted signal is received, the signal requires demodulation in order to recover the data.
Radio receiver architectures commonly employ direct conversion receivers, also known as zero-IF receivers, to perform the demodulation of a received signal. A local oscillator operating at the carrier signal frequency is used to mix down the received signal to produce in-phase (I) and quadrature (Q) baseband signals. The direct conversion receiver converts the incoming carrier signal directly to baseband, in both I and Q components, without use of any intermediate frequencies. Such direct conversion receiver implements a baseband processor which may have a DC offset compensation module and a bit synchronization module.
Bit synchronization arrangement techniques for a radio receiver often include sampling the signal at a constant rate and then normalizing the sampled signal. The adjacent normalized samples are compared to detect the positions of the transitions between signaling levels. The positions of the transitions are recorded and a buffer or counter associated with each position is incremented. For each received bit, the buffer location containing the most transitions is selected and the bit clock may be readjusted.
Another way to synchronize bits is through zero crossing based synchronization algorithms. However, such methods have certain disadvantages such as variation in the output when zero crossings occur during every bit time interval. Further, such techniques have bandwidth limitations, and mismatches between the transmitter and receiver clocks tend to cause the relative positions of the zero-crossing to drift over time.
Therefore, there is a need for an enhanced method and system for bit detection and synchronization.